This invention relates to polyblends of rubbers with styrene/acrylonitrile-type copolymers which are commonly known as ABS compositions, and more particularly to an ABS polyblend and process for forming same which contains a special ABS intermediate.
As typically disclosed in U.S. Pat. Nos. 3,509,237, and 3,652,721, ABS polyblends containing two rubber graft copolymers of different average particle sizes dispersed in ungrafted matrix copolymer which may have the same chemical composition as that of the graft phase of the rubber graft copolymers provide the blend with a highly desirable balance of performance properties. Such polyblends are considered to have a bimodal distribution of rubber graft particles, by which is meant that a plot of frequency versus rubber graft particle size exhibits two distinct peaks. U.S. Pat. No. 4,009,227 discloses such an ABS polyblend containing two graft copolymers of different average particle diameters, and further discloses that the weight ratio of polymerized styrene(S) to polymerized acrylonitrile (AN) in the large particle size rubber graft copolymer should be greater than such ratio in the ungrafted matrix copolymer. This U.S. Pat. No. 4,009,227 also typically discloses compositions, such as in Example 2, having a weight level of AN in the graft phase of the rubber graft copolymers which is less than the weight level of AN in the ungrafted matrix copolymer. However, when preparing these compositions by following, for example, U.S. Pat. No. 4,009,227, the mismatch between the level of polymerized acrylonitrile in the dispersed rubber graft copolymer(s) versus that in the ungrafted matrix is achieved by blending two or more separately prepared, different polymers, which, it is believed, have essentially matched weights of styrene and acrylonitrile in the graft phase and in the ungrafted matrix. It would be desirable to achieve this advantageous mismatch in a less complicated manufacturing system not requiring manipulation in a blending step of proportions of graft copolymers having individually matched graft phase and matrix levels of polymerized styrene and acrylonitrile, but which differ in particle size from each other.
As disclosed in U.S. Pat. No. 4,417,030, it is desirable to form ABS polymers by continuous mass polymerization, but the products therein disclosed are not described as having a weight mismatch between the graft phase and matrix components.